Electrodialytic apparatus



Sept. 21, 1954 p, KOLLSMAN 2,689,826

ELECTRODIALYTIC APPARATUS Filed July 2l, 1950 2 Sheets-Sheet 1 n QI'Ill/1111 INVENTOR. Pa/ Ko smc/'7 BY #rm&.wl

Patented Sept. 21, 1954 UNITED sTATss, ATsNT OFFICE ELEcTRoDIALYTIcAPPARATUS Paul nousmaNew York, N. Y.

Application July 21, 1950, Serial No. 175,127 s claims; (o1. 2114-301)This invention relates to the art of modifying the chemical compositionof substances by a transfer of ions under the influence of an electriccurrent in a process commonly called electrodialysis.

Basically, this process involves a transfer, or removal, of ions of onevolume of fluid through anion impeding and cation impeding dia- `phragmsinto another volume of iiuid under the influence of` an electrical biasor potential causing the ions to travel in predetermined directions. Thevolume of the rst iiuid is thus depleted of ions and the volume of thesecond fluid is enriched.

It is thus possible, for example, to reduce the salt content of salinesolutions, for example, sea water, to a point where the desalted productis suitable for industrial and agricultural uses, and even for humanconsumption.

The present invention provides improvements in, and refinements of, themethod of electrodia'lysis as well as of apparatus for practicing themethod, making method and apparatus more efficient, resulting inproducts of higher purity, and greater uniformity, even with dia-lysisdiaphragms of moderate quality.

'by drawings, showing, for the purpose of illustration, apparatus forpracticing the invention.

The invention also consists of certain new and original features ofconstruction and combination of parts, as well as of steps andcombination `of steps, as hereinafter set forth and claimed.

Although the characteristic features of this invention which arebelieved to be novel will be particularly pointed out in the claimsappended hereto, the invention itself, its objects and advantages, andthe manner in which it may .be carried out will be better understood byreferring to the following description taken in connection with theaccompanying drawings forming a part 4of it, in which:

Figure 1 is a diagrammatic representation, in vertical cross section ofan improved apparatus embodying the present invention and adatped to`carry out the improved method disclosed herein; and

Figure 2 is an elevational view taken on line 2-2 of Figure 1, andshowing, in addition, further details of the apparatus.

In the following description and in the claims various details will beidentified by specific names for convenience. Like reference charactersrefer to like parts in the several figures of the drawings.

In the drawings accompanying and forming a part of this specication,certainspecic disclosure of the invention is made for the purpose ofexplanation of the broader aspects of the invention, but it isunderstood that the details may be modified in various respectswithoutdeparture from the principles of the invention and that the inventionmay be applied to, and practiced by, other structures than the onesshown.

The principles and features of the invention are readily understood byrst considering the basic structure of an apparatus for practicing it.Figure l is a diagrammatic illustration of an apparatus particularlydesigned for increasing and decreasing the salinity of water byclectrodialysis, but it may be used for the treatment or production ofother fluids and compositions.

A tank II is subdivided into a plurality of chambers or cells byseparating ion discriminating walls or diaphragms composed of a suitablecomposition or material imparting to the walls or diaphragme iondiscriminating characteristics. Thus, certain diaphragms I2 areanion-permeable V and cation-repellent, While other diaphragms I3 havetheopposite characteristic of being cation-permeable andanion-repellent. rThe diaphragms are arranged in alternating sequencewith respect to traverse of the tank from one end to the other so thatan anion-permeable diaphragm follows a cation-permeable diaphragm andis, in turn, followed by an anion-permeable diaphragm, and so forth.

The chambers of cells may be classified into two terminal cells Il andI5 containing electrodes I6 and il, and a plurality of intermediatecells I8 and I9.

The electrode Iii `is connected to the negative pole of a source ofelectric energy 2li by a lead 2i thus becoming a cathode, and theelectrode Il is connected to the positive pole of a source 2i) by a lead22 making the electrode Il an anode. The intermediate cells I8 mayconveniently be termed concentration cells, and the intermediate cellsI9 may `be called dilution cells, according to the character of theelectrodialytic action taking place therein.

The dilution cells I 9 are preferably narrower than the concentrationAcells I8, width being measured between the bordering diaphragms.

Speaking first of the dilution cells I9, the cells have inlet ports 23at, or near, the bottom admitting fluid into the dilution cells from aninlet duct 24 which is suitably manifolded with respect to all thedilution cells.

The endmost diaphragms extend above the tops of the intermediatediaphragms to corinne between them a common pool 25 with which the openends 26 of the cells I9 communicate freely. A large outlet port 2ldetermines the height to which the liquid level 28 may rise. An outletduct 29 (Figure 2) leads from the port 2l to discharge processed uidfrom the processing tank II.

The terminal diaphragms have ports 30 and 3| controlled by adjustablegate members 32 and 33 for admission of a controlled volume of iiuidfrom the pool 25 into the terminal chambers I4 and I5 which the fluidleaves through ducts 34 and 35'.

Fluid in the pool may freely enter the concentration chambers I8 whichare open at the top at 36. The fluid iiows through the concentrationchambers in a downward direction, opposed to the direction of flowthrough the chambers I8, and leaves the concentration chambers throughrestricted metering passages 3l which form discharge ports for thesechambers. The restricted passages 31 are dimensioned to permit only afraction of the volumetric iiow admitted through the inlet ports 23 topass into a common discharge duct 43 as will also be explained later ingreater detail.

The `fluid of the terminal chambers is preferably handled separatelybecause of certain electro-chemical reactions which may be induced bythe physical presence of the electrodes in the chambers, making itgenerally undesirable to mix the product of the terminal cells with theproducts of other cells.

From the arrangements of the ports, ducts and cells or chambers it isevident that the direction of flow through the dilution cells isupwards, or opposed to gravitation while the direction of iiow throughthe concentration cells is downward following gravity.

Fluid is supplied through the inlet duct 24 at a predeterminedcontrolled slow rate which is maintained sufliciently slow to insure apre- `determined degree of dilution, by reason of iondepletion, to takeplace, during the ow of the fluid from the bottom of the cells to thetop.

The flow through the concentration cells is preferably maintained at afraction of the total volumetric flow passing through the dilutioncells, a preferred range of ratios being that in which the ow throughthe concentration cells is restricted to between one-half andone-twelfth the volumetric flow passing through the dilution cells. Thisis preferably accomplished by installation of flow restricting passages31 of the proper dimension.

Since most electrodiallytic processes involve a transfer of a certainamount of uid through the diaphragms it is convenient to compare thevolumetric flows through the dilution and the concentration cells byreference to the volume entering the dilution cells through the inletduct 24 and to the volume leaving the concentration cells through thedischarge duct 43 into which the restricted passage 31 lead. Thus thevolume of fluid entering the dilution cells includes that portion offluid which permeates the diaphragms of the dilution cells, and thevolume withdrawn from the concentration cells includes 4 the fluid gaindue to passage of fluid through the diaphragms into the concentrationcells.

The supply of fluid through the inlet duct 24 may conveniently bemaintained at a predetermined volumetric rate by use of supply tank 38(Figure 2) connected to the duct 24. The liquid level 39 in the supplytank is maintained constant by a supply valve 4I) controlled by a iioat4I admitting sufcient fluid from a supply pipe 42 to maintain the liquidlevel slightly above the liquid level 28, the difference in the twolevels being so selected as to provide for a predetermined staticpressure which, in turn, results in a predetermined rate of flow throughthe chambers I9. It is thus possible to control the rate of ilow throughthe dilution cells by adjustment of the float 4I.

The operation of the apparatus may be conveniently explained by a specicexample. It may be assumed that the apparatus is being used for theproduction of fresh water of a high degree of purity and thesimultaneous production of concentrated sea water or brine. When theoperation of the device as applied to Water purification is understood,it will easily be seen how other compounds in solution may be treated inthe apparatus.

It may be assumed that an electrical potential is applied at theelectrodes at the time salt-containing raw water enters through theinlet duct 24 into the apparatus whose concentration cells are alsofilled with water, preferably containing a slight amount of salt inorder to cause a current to ow through the cells from one electrode tothe other. The raw water fed into the apparatus is preferably rstfiltered to free it from mechanical impurities. The raw water ows slowlythrough the dilution cells from the bottom towards the top and isgradually deionized by reason of the action of the electric currentcausing the ions of the raw water to permeate the diaphragms.

Assuming, for reasons of simplicity, that the only salt present in theraw water is sodium chloride, the positively charged sodium cations tendto travel towards the cathode I5. The sodiu'm cations pass through thecations permeable diaphragms I3 and accumulate in the concentrationcells I8 which they are unable to leave because of the cation-blockingproperties of the diaphragms I2 which bar their path.

Similarly chlorine anions pass through the anion permeable diaphragm I2and accumulate in the concentration cells I3 from which their exit isbarred by the anion-blocking properties of the diaphragms I3.

The sodium and chlorine ions in the concentration cells recombine assodium chloride and cause the salt concentration in the cells I3 toincrease, while simultaneously the salt concentration in the dilutioncells decreases.

Since purified water is present in the pool 25 during normal operationof the apparatus, the purication of water flowing through the dilutioncells may be carried to a very high degree, and Water leaving throughthe outlet port 2l has a particularly high degree of purity.

The flow through the concentration cells takes place at a volumetricrate which is only a fraction of the volumetric rate of flow through thedilution cells. For this reason the salt enrichment per volumetric unitof fluid in the concentration cells reaches a higher degree than thesalt depletion in the dilution cells. Assuming, .for example, that thevolumetric ilow through the 5, concentration cells is one sixth of thevolumetric :dow through the dilution cells,.itlis evident Vthat theconcentration taking place` in the concentration compartment `is sixtimes as great per volumetric unit of fluid as the loss of salt in thedilution cells so that the water leaving the concentration `compartmentthrough the discharge ports contains six times the amount of salt as thesea water entering the dilution cells.

The aforementioned iiowand concentration ratios involve several economicadvantages. Firstly, it seems that `the transfer of fluid, or. in otherwords, the loss of water by passage from the dilution compartments intothe concentration compartments at any particular point of the diaphragmis, in approximation inversely proportional to the concentration on theother side of the diaphragm at the :point Where the loss occurs.

Since, furthermore, the loss of fluid appears to be proportional to thetransfer of ions, the presence of a higher ion concentration near thebottom of the concentration cells lessens the loss of fluid from thedilution cells in which the greatest loss also tends to occur near thebottom. Thus the high ion concentration in the concentration cells tendsto reduce the loss of fluid from the dilution cells.

The high concentration of the fluid leaving the concentration cellsmakes the fluid suitable for further commercial use, which it might nothave, if the concentration were less. Thus the resultant brine may beused for manufacture of dry salt and other uses.

In addition, greater economy is achieved due to the `fact that the iiuidin the cells I 8 offers little resistance to electric current because ofthe high concentration by reason of he reduced volumetric rate of flow.

It is easily seen that the ion depletion in the dilution cells per inchof advance from the inlet ports 23 to the pool 25 proceeds at a slowerlinear rate than the ion enrichment per inch of advance from the pool 25to the discharge ports 31.

The volumetric rate of flow through the dilution cells I9 may becontrolled either by control of the fluid pressure or by the dimensionsof the ports 2l, or both, in such a way that the fluid leaving thedevice through the outlet lduct 29 has the desired degree of dilution,and the volumetric flow through the concentration compartment is socontrolled, as to maintain the ion enrichment at a predetermined ratiowith respect to the ion depletion in the adjoining cells. For example,the ratio may be one to six or one to ten, or any other gure, asconditions `may require. This is conveniently effected by control of theout-flow, for example by installation of suitably restricted dischargeports 2B.

A particular feature of the counter flow arrangement of the illustratedapparatus is its favorable effect on the current density near the bottomof the cells in order to remove the greatest possible number of ions perunit of time from the ilow entering the dilution cells. A high currentdensity near the bottom of the cells is promoted by the concentrationcells in which the greatest concentration and hence the :greatestconductivity is likewise near the bottom, and not near the top, as itwould be in an `installation which does notemploy the principle ofopposite ilow on opposite sides of the diaphragms.

The rate of flow through the individual dilution cells is controlled inAsuch a way that the product at the tops 2.6 of "all the cells `Il) is of6. uniform purity. It is rather di'icult to control the `rate of flowthrough the individual dilution cells E9 by proper dimensioning of theirindividual inlet ports 23 in such a way that the volumetric flowsthrough all the dilution cells I9 is `precisely the same. Nonmuniformityof flow has certain disadvantages, as will be seen from the followinspecific examples:

`It may be assumed, that the volumetric ilow through all the cells isequal with the exception of one cell through which the ow passes at aslower rate. Under these circumstances all the cells, except the one,yield a product of insufficient purity, since the uid in the one cellbecomes deionized sooner than the fluid in the other cells. As soon asthe fluid in the one cell becomes deionized its conductivity' approacheszero and the current ceases to flow. Deionization in the other cellsceases, and the fluid discharged from them has a lower degree of purity,than desired. I

A similar result is obtained if the rate of flow through all the cellsis the same, but the fluid passing through one oi the cells happens tohave a lower initial ion content than the fluid in the others. In thiscase deionization is completed too soon in the one cell and the fluid inthe other cells is insufliciently deionized because the current ceasesto ow.

In these two examples, it should be understood that reference is made tothe flow of current at a certain level above the bottom of the cells,since obviously current will still continue to flow near the bottomwhere the ion content of the flows is sufficiently great. However, nearthe top of the dilution cells the current density becomes so low uponcomplete deicnization of the fluid in one or a few cells near the topthat the electrodialytic action ceases in all the other cells atapproximately the same level, at which, due to the higher initial iiowrate or the higher initial ion concentration the fluid has not yetreached the state of complete deionization.

These undesirable conditions may be eliminated or reduced by anautomatic control of the flow through the individual cells in dependenceon the gravity of the fluid in the respective cell.

Due to the relatively slow rate of flow in the illustrated form ofapparatus and due to the fact that the pressures at all the inlet ports23 and at the tops 2@ of the dilution chambers are equal, the gravitycontrol may be carried out in an extremely simple manner by using theweight of the liquid columns as the controlling means. In other words,the specic gravity of each fluid column proper in the individualdilution cells retards or accelerates the flow through the cells. It hasbeen found that extremely small differences in gravity are suificient toprovide a very effective control of the rate of flow. The controloperates as follows:

It may be assumed that the fluid ows at a more rapid rate through onecell than through the other. In this case the rapid flow in the one cellcauses the iluid to be exposed to the dialyzing current for a shortertime than in the other cells, resulting in less deionization and ahigher specic gravity of the fluid in the one cell than in the others.The greater weight of the fluid column in the one cell causes less liuidto enter the cell, thus retarding the flow. The retarded iicw is subjectto the dialyzing current for a longer period of time whereby aproportionately greater number of ions is removed therefrom, causing theweight of the fluid column to become less and the ow rate to increase.In this manner a proper mean rate of flow is automatically maintained ineach cell resulting in a yield of fluid from all the dilution cellswhich is of substantially uniform purity,

If a fluid of a particularly high degree of purity is desired, forexample, if drinking water is to be produced from sea water, it ispreferable to subject the iluid to the action of a dialyzing currentmore than once. I am aware that it has formerly been proposed to treatfluids in successive stages to produce a product of great purity.However, the present modification of the basically known idea ofstage-by-stage operation, involves several novel and advantageousaspects, which result in an improvement over conventional and knownoperations.

In the apparatus disclosed herein the same dialyzing current flowsthrough all the dilution cells and an equal number of ions are drivenout of all the dilution cells within a predetermined period of time.Unequalities in the degree of purity of the output is largelycounteracted by the effective flow control, hereinbefore described.However for very exacting demands the effect of the variations in thepurity of the output of the individual dilution cells is eliminated, anda higher total degree of purity is attained in a rather economicalmanner by the arrangement illustrated more particularly in Figure 2.

The product of all the dilution cells I9 is collected in the pool 25 andwithdrawn through the port 21 and the duct 29. The now of the treatedfluid through the duct 29 involves intimate mixing of the products ofthe several dilution cells so that the fluid is of uniform concentrationor dilution as it enters a second dialyzer tank Ill through an inletduct H24. The dialyzer III corresponds in all details to the dialyzershown in Figure 1, but the potential applied to its electrodes may behigher because of the low ion concentration of the iiuids to be treated.A lead l2| leading to the anode of the dialyzer lll is visible. After owof the fluid through the dilution cells of the second dialyzer the fluidis again collected in a pool and is then withdrawn through a duct |29.The fluid obtained at the duct |29 is of a high degree of purity and thesecond step of dialyzation is efflcient and economical, since theproducts of the cells of the rst dialyzer are not individually subjectedto the second treatment, but only after thorough mixing. This isimportant since no unduly high voltages need be employed to overcome theeffects of the presence of a more highly purified product in some of thecells, resulting in a greater ohmic resistance, than in the others.

It will be noted that, aside from the -transfer of ions through thediaphragms, no electrochemical electrode rea-ction takes place in any ofthe intermediate cells, since the cells do not contain electrodes.

The electrodes IB and I1 are lmade of a material resistingdecomposition. Carbon and graphite are suitable materials for theanodein an apparatus for purifying wa-ter, and iron or nickel-chromiummay serve as material for the cathode.

Since the dilution cells represent a greater ohmi'c resistance per unitof width than the concentration cells, -the dilution cells may be madenarrower than the concentration cells.

In actual practice the thickness of the fluid lms in the ycells isconsiderably less than shown in the drawings in which many dimensionsare exaggerated or reduced for the sake of clearness. It has been foundparticularly advantageous toA make the spaces between the diaphragmsnarrower than the thickness of the diaphragms and to employ diaphragmsof high electric conductivity. For example, a spacing of one or twomillimeters has 'been found advantageous `for diaphragms of a thicknessof three millimeters.

Similarly, the height of the cells is not shown in its correct-proportion with respect to the other dimensions. The height of theycells may natu` rally be considerably greater than shown so that thefluid columns in the cells are of substantial length.

In the practice of the improved method of electrodialysis flows of fluidto be deionized are confined between flows of fluid into which ions areto be transferred through ion-discriminating diaphragms. The fluids aremaintained in ythe state of flux in opposite directions `past thediaphragms and the volumetric flow of the iiuid into which ions are tobe transferred' is maintained smaller than -the volumetric flow of theiiuid to be deionized. By this arrangement the concentration on bothsides of the diaphragm is greatest near the bottom of the cells and thefluid transfer -through the diaphragms is minimized as hereinbefore setforth.

The volume of fluid withdrawn from the `concentration cells may besupplied in part from the output of the dilution cells, but may bereplenished entirely by fluid transfer through the diaphragms. It isevident that in the treatment of fluids in steps or stages by passage,in succession, through several ion exchange units as represented byFigures 1 and 3, the fluid supplied to the concentration cells in therst stage or unit need not be as highly purified as in the succeedingstages, since the purity of the fluid at the top of the concentrationcells need not be greater than the desired purity of the iiuid leavingthe dilution cells.

Referring -to the illustrated forms of apparatus, it is seen that theflow of iiuid to be deionized is split into a plurality of substantiallyequal branches all of which are subjected to the same current. Itfollows that the rate of deionization per inch of flow is the same inall -the branches assuming that the flows are equal. This isconveniently -controlled by proper adjustment of the individual portslthrough which the fluid enters or leaves the cells.

Thus numerous changes, additions, omissions, substitutions andmodifications in the apparatus and `method steps, as well as otherapplications of the method and apparatus may be made withou-t departingfrom the spirit, the teaching iand the principles of the invention.

For the sake of brevity the term ion-discriminating diaphragm is used inthe claims to identify membranes which have the inherent property ofbeing permeable to ions of one sign and passage resistant to ions of theopposite sign.

What is claimed is:

l. An apparatus for increasing and decreasing the ion ycontent ofliquids, comprising means forming a plurality of chambers, not less thanve, the -chambers being arranged in line; aniondiscriminating andcation-discriminating `diaphragms between said chambers for establishinga selective path for ions from one chamber into an adjoining ichamberunder the inuence of an electrical potential, said diaphragms beingarranged in substantially vertical position and in alternating sequencewith respect to traverse from one terminal chamber through theintermediate chambers to the other terminal cham-.

ber; an electrode in each of the terminal cham bers, one electrode toserve as an anode, the other electrode to serve 'as a cathode; meansincluding inlet ports near the bottom of certain alternate `chambers forsupplying raw liquid to be deionized into said alternate chambers; meansforming a common space above, and in communication With, all of saidintermediate chambers, said common space lying above the upper ends ofsaid diaphragms for collecting liquid from said alternate chambersrising into said common space by reason of flow and lreduced specicgravity, said common space having an overflow outlet port above the topsof the diaphragms through which deionized liquid may be withdrawn; meansincluding discharge ports near the rbottom of other -chambers lyingbetween said alternate lchambers for discharging concentrate from saidother chambers, liquid from said common space entering said otherchambers at points above the level of said discharge ports, whereby theflow through said other chambers is substantially opposed in directionto the ow through said alternate chambers.

2. An apparatus for increasing and decreasing the ion content ofliquids, comprising means forming a plurality of chambers, not less thanve, the chambers being arranged in line; aniondiscriminating andcation-discriminating diaphragms between said chambers for establishinga selective path for ions from one chamber into an adjoining chamberunder the inuence of an electrical potential, said diaphragms beingarranged in substantially vertical position and in alternating sequencewith respect to traverse from one terminal chamber through theintermediate chambers to the other terminal chamber; an electrode ineach of the terminal chambers, one electrode to serve as an anode, theother electrode to serve as a cathode; means including inlet ports nearthe bottom of certain alternate chambers for supplying raw liquid to bedeionized into said alternate chambers; means forming a common spaceabove, and in communication with, all of said intermediate chambers,said common space lying above the upper ends of said diaphragms forcollecting liquid from said alternate chambers rising into said commonspace by reason of flow and reduced specific gravity, said common spacehaving an overow port above the tops of the diaphragms through whichdeionized liquid may be withdrawn; means including discharge ports nearthe bottom of other chambers lying between said alternate chambers fordischarging Iii concentrate from said other chambers; and meansincluding supply ports for admitting liquid from said common space intosaid terminal chambers.

3. An apparatus for increasing and decreasing the ion content ofliquids, comprising means forming a plurality of chambers, not less thanfive, the chambers being arranged-in line; aniondiscriminating andcation-discriminating diaphragms between said chambers for establishinga selective path for ions from one chamber into an adjoining chamberunder the iniiuence of an electrical potential, said diaphragms beingarranged in substantially vertical position and in alternating sequencewith respect to traverse from one terminal chamber through theintermediate chambers to the other terminal chamber; an electrode ineach of the terminal chambers, one elecl trode to serve as an anode, theother electrode to serve as a cathode; means including inlet `ports nearthe bottom of certain alternate chambers for supplying raw liquid to bedeionized into said alternate chambers; means forming a common spaceabove, and in communication with, all of said intermediate chambers,said common space lying above the upper ends of said diaphragms forcollecting liquid from said alternate chambers rising into saidcollection chamberby reason of flow and reduced specific gravity, saidcommon space having an overflow outlet port above the tops of thediaphragms through which deionized liquid may be withdrawn; meansincluding discharge ports near the bottom of otherl chambers lyingbetween said alternate chambers for discharging concentrate from saidother chambers; and means for admitting liquid from said common spaceinto the terminal electrode-containing chambers; and means separate anddistinct from said outlet port and said discharge ports for dischargingliquid from said terminal chambers.

References Cited in the iile of this patent UNITED STATES PATENTS NumberName Date 1,326,106 Schwerin Dec. 23, 1919 1,546,908 Lapenta July 21,1925 1,986,920 Cross Jan. 8, 1935 2,411,238 Zender Nov. 19, 19462,636,852 Juda et al Apr. 28, 1953 OTHER REFERENCES Helvetica ChimicaActa, vol. 23 (1940), pages 795 thru 800.

Journal of The Electrochemical Society, vol.

` 97, No. 7, July 1950, pages 139C thru 151C.

"Journal of Physical and Colloid Chemistry,` vol. 54 (1950), pages 204thru 226.

1. AN APPARATUS FOR INCREASING AND DECREASING THE ION CONTENT OFLIQUIDS, COMPRISING MEANS FORMING A PLURALITY OF CHAMBERS, NOT LESS THANFIVE, THE CHAMBERS BEING ARRANGED IN LINE; ANIONDISCRIMINATING ANDCATION-DISCRIMINATING DIAPHRAGMS BETWEEN SAID CHAMBER FOR ESTABLISHING ASELECTIVE PATH FOR IONS FROM ONE CHAMBER INTO AN ADJOINING CHAMBER UNDERTHE INFLUENCE OF AN ELECTRICAL POTENTIAL, SAID DIAPHRAGMS BEING ARRANGEDIN SUBSTANTIALLY VERTICAL POSITION AND IN ALTERNATING SEQUENCE WITHRESPECT TO TRANVERSE FROM ONE TERMINAL CHAMBER THROUGH THE INTERMEDIATECHAMBERS TO THE OTHER TERMINAL CHAMBER; AN ELECTRODE IN EACH OF THETERMINAL CHAMBERS, ONE ELECTRODE TO SERVE AS AN ANODE, THE OTHERELECTRODE TO SERVE AS A CATHODE; MEANS INCLUDING INLET PORTS NEAR THEBOTTOM OF CERTAIN ALTERNATE CHAMBERS FOR SUPPLYING RAW LIQUID TO BEDEIONIZED INTO SAID ALTERNATE CHAMBERS; MEANS FORMING A COMMON SPACEABOVE, AND IN COMMUNICATION WITH, ALL OF SAID INTERMEDIATE CHAMBERS,SAID COMMON SPACE LYING ABOVE THE UPPER ENDS OF SAID DIAPHRAGMS FORCOLLECTING LIQUID FROM SAID ALTERNATE CHAMBERS RISING INTO SAID COMMONSPACE BY REASON OF FLOW AND REDUCED SPECIFIC GRAVITY, SAID COMMON SPACEHAVING AN OVERFLOW OUTLET PORT ABOVE THE TOPS OF THE DIAPHRAGMS THROUGHWHICH DEIONIZED LIQUID MAY BE WITHDRAWN; MEANS INCLUDING DISCHARGE PORTSNEAR THE BOTTOM OF OTHER CHAMBERS LYING BETWEEN SAID ALTERNATE CHAMBERS,FOR DISCHARGING CONCENTRATE FROM SAID OTHER CHAMBERS, LIQUID FROM SAIDCOMMON SPACE ENTERING SAID OTHER CHAMBERS AT POINTS ABOVE THE LEVEL OFSAID DISCHARGE PORTS, WHEREBY THE FLOW THROUGH SAID OTHER CHAMBERS ISSUBSTANTIALLY OPPOSED IN DIRECTION TO THE FLOW THROUGH SAID ALTERNATECHAMBERS.